The field of invention is the treatment of conditions concerned with peripheral vasoconstriction. More particularly, the invention is concerned with methods for establishing normal vascular tone in regions of the circulation which demonstrate pathophysiology. In particular, the invention concerns a method of treating erectile dysfunction by provision of nitric oxide, nitric oxide producing agents, or activators of guanyl cyclase in small doses or microdoses, i.e., doses that do not induce undesirable side effects, such as systemic vasodilation, under normal conditions.
It is widely known that administration of nitric oxide (NO), or compounds which deliver NO (i.e., NO donors, NO producing agents) to a subject, can provoke powerful vasodilator responses. Such administration is often accompanied by a number of undesirable side effects which include headache, flushing, and hypotension.
The physiological role of NO has been described as that of a powerful chronic vasodilator agent based on there being a marked increase in vascular tone following NO synthase (NOS) blockade (Johnson et al., Am. J. Hypertens. 5:919, 1992; Tolins et al., Hypertens. 17:909, 1991). The role of NO as a chronic vasodilator has only been inferred by indirect means, i.e., by removal of NOS activity. Endogenously, much more multiplicity and overlap in the control of vasodilation can be inferred from the scientific literature. For example, vasodilation can be induced by acetylcholine, bradykinin, adenosine, adenosine triphosphate (ATP), histamine, vasoactive intestinal polypeptide (VIP), and leukotrienes, amongst others. The actions of these endogenous modulators have been shown to be dependent, at least in part, on the presence of the endothelium, an effect likely mediated by endothelial derived relaxing factor/NO (EDRF/NO) (Garg, U. C. et al., J. Biol. Chem. 266:9, 1991; Garg, U. C. et al., J. Clin. Invest. 83:1774, 1989; Palmer, R. M. J. et al., Nature 327:524, 1987). Other vasodilator mechanisms exist which are not endothelium dependent, such as xcex22-adrenergic receptor activation, atrial natriuretic peptide (ANP) and certain prostaglandins. The actions of NO have been suggested to be mostly cGMP-mediated via guanylate cyclase activation, although other mechanisms have been suggested. For example, Garg et al. (J. Biol. Chem. 266:9, 1991; J. Clin. Invest. 83:1774, 1989) and others (Assender, J. W. et al., J. Cardiovasc. Pharmacol. 17(Suppl.3):S104, 1991; O""Conner, K. J. et al., J. Cardiovasc. Pharmacol. 17(Suppl.3):S100-S103, 1991) demonstrated a difference in the effects of NO-generating vasodilator agents in inhibiting vascular smooth muscle cell growth in culture; however, it is clear that NO can act not only as a vasodilator but also to inhibit vascular growth responses in a number of conditions (Farhy, R. D. et al., Circ. Res. 72:1202, 1993).
It has been believed and widely practised that NO, in humans and animals, produced via sodium nitroprusside (SNP) infusion, causes vasodilation in peripheral vasculature at doses greater than 10 xcexcg/kg per min. It has recently been determined that NO also performs a function through interaction with endothelin (ET) (Banting et al., J. Hypertens. 14:975, 1996; Richard et al., Circulation 91:771, 1995). Prior to this time, ET had been believed to play a minimal role in maintaining tone in the peripheral microvasculature and to have little impact on the state of contraction of smooth muscle in those vessels. Recent studies have indicated (Banting et al., J. Hypertens. 14:975, 1996) that ET is under the inhibitory control of NO and that administration of NOS inhibitors results in elevated levels of ET.
Endothelins were first described in 1988 and have been shown to be powerful vasoconstrictors, predominantly found in vascular endothelium and, since that time, numerous ET antagonists and their pharmaceutically acceptable salts have been identified and can be obtained commercially (e.g., Sigma, American Peptides). Detailed descriptions of the chemical structures of various ET antagonists may be found in U.S. Pat. No. 5,284,828 issued Feb. 8, 1994 to Hemmi et al., U.S. Pat. No. 5,378,715 issued Jan. 3, 1995 to Stein et al., and U.S. Pat. No. 5,382,569 issued Jan. 17, 1995 to Cody et al. In addition, U.S. Pat. No. 5,338,726 issued Aug. 16, 1994 to Shinosaki et al. describes the chemical structure of ET converting enzyme inhibitors. To date, however, antagonists of ET have not been approved for therapeutic use, although a number of investigators have postulated that ET antagonists could be used for conditions ranging from renal failure, endotoxic shock, asthma, angina, or diabetes to pulmonary hypertension and possibly other indications.
Under normal physiological conditions, ET can be found in almost all parts of circulation at very low levels. In general, in the normal rodent circulation ET is not found in elevated quantities and appears to have little detectable role in the normal regulation of vascular tone, i.e., there is no appreciable decrease in blood pressure when an ET antagonist is administered by injection in normal circulation. Further, at present there does not appear to be any evidence suggesting that ET plays a physiological role even in a small portion of the circulation under normal circulatory conditions in experimental models. However, it is likely that the systemic circulation may appear to be normal when, in fact, specific regions of the circulation are undergoing pathophysiological changes such as occurs in conditions such as erectile dysfunction (ED) (Adams et al., Int. J. Impot. Res. 9:85-91, 1997).
Consequently, there are cardiovascular conditions which are traditionally treated in human beings by significant doses of NO or NO donors, such as glyceryl trinitrate (GTN) (0.2 mg/h and greater). However, these doses are known to induce systemic vasodilation and provoke considerable overall systemic side effects (The, L. S. et al., Brit. J. Rheum. 34:636, 1995). This is particularly so where a pathological condition exists only in certain major organs (e.g., heart, kidney, liver). As a result, a satisfactory method for promoting recovery of normal perfusion pressure in organs with certain pathologies without producing overall systemic hypotension has not been discovered.
Based on the understanding that a significant portion of underlying problems in clinical erectile dysfunction relates to xe2x80x9cvascularxe2x80x9d mechanisms, much of the current state-of-the-art research involves determining the contribution that the different vascular effector control systems make in normal and pathophysiological states. There is substantial understanding of hemodynamic events that lead to an erection, and yet the quantitative roles of each of the neuroeffector, humoral and local systems in these events remain poorly described. Since 1990, NO has been considered the primary non-adrenergic non-cholinergic neurotransmitter in the penis and has been presumed to be the primary mediator of corporal relaxation during erection (Ignarro L. J. et al., Biochem. Biophys. Res. Comm., 170:843, 1990).
It is well established that, for an erection to occur, neurally mediated (autonomic) vasodilation of the penile arterial blood vessel and the trabecular meshwork takes place (Lue, T. F. et al., J. Urol. 137(5):829, 1987) permitting increased blood flow into the cavernous bodies of the penis. The expanding intra corporal volume compresses the effluent veins that lie between the erectile tissue and the surrounding fibrous, relatively inelastic, tunica albuginea. The outflow capacity is thereby decreased and entrapment of blood ensues, resulting in the transformation of the flaccid penis into its erect state (Lue, T. F. et al, J. Urol. 137(5):829, 1987; Juenemann, K. P. et al., J. Urol. 136(1):158, 1986; Lue, T. F. et al., J. Urol. 130:1237, 1983; Weiss, H. et al., Ann Intern. Med. 76:793, 1980). The level of arterial vascular tone (i.e., blood pressure) is one of critical importance in this process, although adequate perfusion pressure is also a necessary factor. The converse, detumescence, is mediated by the sympathetic nervous system (Saenz de Tajada, I. et al., Am. J. Physiol. 254:H459, 1988; Juenemann, K. P. et al., Br.J. Urol. 64, 1989).
The issue of xe2x80x9cimpotencexe2x80x9d (defined as xe2x80x9ca pattern of persistent or recurrent inability to develop or maintain an erection of sufficient rigidity for successful coitusxe2x80x9d) was discussed at a consensus conference of the National Institutes of Health (NIH) in Washington in December 1992 and has been clearly identified as having a wide range of causative or associated factors. The Massachusetts Male Aging Study (MMAS) has provided an updated view of the epidemiology of erectile dysfunction. It is accepted that the prevalence of impotence increases with age (Kinsey A. C. et al., xe2x80x9cSexual Behaviour in the Human Malexe2x80x9d, W. B. Saunders: Philadelphia, 1948). Severe or complete ED increases from 5 to 15% between 40 and 70 years of age, (Feldman, H. A. et al., J. Urol. 151:54, 1994). ED has been shown to be xe2x80x9cdirectly correlated with heart disease, hypertension, diabetes, associated medications, indices of anger and depression, and inversely with serum dehydroepiandrosterone, high density lipoprotein, cholesterol and an index of dominant personality.xe2x80x9d
It is now estimated that in North America there are more than 30,000,000 men with some form of ED, a significant increase from the figure of 10,000,000 quoted just 10 years ago (Shabsigh, R. et al., Urology 32:83, 1988; Whitehead E., Geriatrics 43(2):114, 1988; Furlow, W. L. et al., Med. Aspects Human Sexuality 19:13, 1985). From these figures it is also reasonable to estimate that as many as three million Canadian men may have a degree of ED. The direct cost of treating impotence is significant. Reliable figures from 1985 show that the cost of treating impotence exceeded 146 million dollars in the United States in that year alone (National Center for Health Statistics) and this number is just the estimated market size for one type of injectable therapy. The secondary effects and indirect costs associated with ED suggest that impotence and sexual dysfunction are medical icebergs. The consequences of sexual dysfunction may be seen in strains on the host relationship potentially leading to marital breakdown, violence, work related sequelae, deviant sexual behaviour and impacts on children, when present, that can carry the damage into a new generation of unwanted behaviours. If ED underlies even a small but significant percentage of marital and family breakdown, then it adds vastly to the social and economic burden in society. The pragmatic issue is that large numbers of men are now being treated for ED and most of the treatments are fairly blunt instruments (e.g., intracavernosal injection (ICI)) of mixed vasoactive compounds, penile prosthesis insertion) with significant cost and complications (ICI: pain, priapism, dislike of the technique; prostheses: reoperation, infection, distortion of body image).
Administration of NO, or compounds which are able to deliver NO, have been suggested as possible therapies; however, these agents can provoke powerful yet inappropriate vasodilator responses (Brock et al., J. Urol. 150:864, 1993). Such administration is often accompanied by a number of undesirable side effects related to systemic vasodilation which include headache, flushing, and hypotension. Consequently, there is a real need to provide methods whereby ED and other vascular disease may be quickly and effectively treated without any inappropriate side effects.
Problems associated with localized imbalance in vascular tone, such as seen in ED, and which are hypothesized to be largely due to elevated ET, may be relieved by the administration of agents which are able to provide NO, by direct administration of NO, or by administration of an agent or agents which activates guanyl cyclase, such as, for example, YC-1, or other agents which prolong the actions of endogenous NO or of cGMP (a 2nd messenger molecule), such as phosphodiesterase (PDE) inhibitors, in minimal doses or microdoses, which heretofore had not been thought to result in effective treatment of an imbalance in vascular tone.
In the normal physiological state, there are sufficient quantities of NO present in the vasculature to maintain appropriate levels of ET (Banting et al., J. Hypertens. 14:975, 1996). The addition of further NO has little impact on the effect of ET and consequently any further vasodilation seen in such normal smooth muscle in the vasculature is likely attributable to NO""s effects on the generation of cGMP, with cGMP resulting in decreased levels of Ca++. In certain pathological conditions, such as diabetes and cardiovascular disease, and/or as a consequence of age, tissue is unable to provide satisfactory levels of NO in order to suppress normal levels of ET present in smooth muscle tissues.
As such, physiological conditions where NO production is reduced in a specific local circulation, such as male ED, indicate that suppression of ET activity should offer an effective treatment. Consequently, in accordance with this, the present invention provides for the use of an agent or agents which directly or indirectly generates NO at dosages which are about one half to about one twentieth (xc2xd to {fraction (1/20)}) of those known to induce vasodilation in xe2x80x9cnormalxe2x80x9d circulations, and consequently exert almost no effect in the normal vasculature. As such these low doses, or xe2x80x9cmicrodosesxe2x80x9d are hypothesized to normalize the balance between NO and ET. The range of about xc2xd to about {fraction (1/20)} is derived from the observation that at doses which are below about xc2xd the normal dose, systemic effects are generally no longer seen. At about {fraction (1/20)} the normal dose, however, the desired effect is also generally no longer observed, i.e., there is no effect.
According to one aspect of the present invention the concept of xe2x80x9clow-dosexe2x80x9d agents which directly or indirectly generate NO, or prolong the action of NO, or enhance the cGMP 2nd messenger system, such as PDE inhibitors, is also applicable to any other peripheral pathological conditions where, regardless of the origin, NO is at least partially inhibited.
According to a further aspect of the present invention, there is provided a method for restoring normal vascular tone in vasculature where NO levels are depleted and restoration of such levels may be achieved by addition of NO at levels which do not appreciably alter normal systemic vascular tone.
According to yet a further aspect of the present invention there is provided a method to treat any condition where NO levels are at least partially inhibited or reduced, wherein the method comprises administration of NO or one or more NO donors, or one or more agents which activate guanyl cyclase, by oral, sublingual, buccal, intravenous, transdermal, or any other effective route, in concentrations that are about xc2xd to about {fraction (1/20)} of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature. Preferably, the concentrations of the method of the present invention are about one quarter to about one twentieth (xc2xc to {fraction (1/20)}) of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature. Still more preferably, the concentrations of the method of the present invention are about one eighth to about one sixteenth (xe2x85x9 to {fraction (1/16)}) of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature.
According to one aspect of the present invention there is provided a method to treat instances of renal disease associated with excessive vasoconstriction where NO levels are at least partially inhibited, wherein the method comprises administration of NO or one or more NO donors, or one or more agents which activate guanyl cyclase, by oral, sublingual, buccal, intravenous, transdermal, or any other effective route, in concentrations that are about xc2xd to about {fraction (1/20)} of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions of the circulation such as the coronary or skeletal muscle vasculature.
According to a another aspect of the present invention there is provided a method to treat premature aging of the skin associated with inappropriate vasoconstriction of the skin vasculature which is associated with at least partial inhibition of NO levels in the skin, wherein the method comprises administration of NO or one or more NO donors, or one or more agents which activate guanyl cyclase, by oral, sublingual, buccal, intravenous, transdermal, or any other effective route, in concentrations that are about xc2xd to about {fraction (1/20)} of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature.
According to a further aspect of the present invention there is provided a method to treat male ED caused at least by partial inhibition of NO in the penile vasculature wherein the method comprises administration of NO or one or more No donors, or one or more agents which activate guanyl cyclase, by oral, sublingual, buccal, intravenous, transdermal, or any other effective route, in concentrations that are about xc2xd to about {fraction (1/20)} of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature.
According to yet a further aspect of the present invention there is provided a method to treat ED comprising administering to a subject in need thereof a quantity of glyceryl trinitrate (GTN) by any route, for example, oral, sublingual, transdermal, intravenous, or inhalation, that provides plasma concentrations of below about 250 pg/ml of the GTN, so that ED is treated.
According to one aspect of the present invention there is provided a low-dose transdermal xe2x80x9cpatchxe2x80x9d with short term release of, for example, GTN or any other effective provider of NO, such as, for example, one or more NO donors or one or more agents which activate guanyl cyclase, over a period of time less than 6 hours (as opposed to 12, 18 or 24 hour release), which restores normal vascular tone in an affected local vascular bed, such as the pudendal or penile vasculature of men with ED, without inappropriately affecting systemic vascular tone or causing hypotension, and preferably, but not necessarily, without inducing tolerance (Bennett et al., Circ. Res. 63:693, 1988) to the effects and/or biotransformation of a NO releasing compound to its releasing form.
According to a further aspect of the present invention, there is provided a low dose or microdose xe2x80x9cpatchxe2x80x9d with long term release of, for example, GTN, or any other effective provider of NO, such as, for example, one or more NO donors, or one or more agents which activate guanyl cyclase, over a period of time greater than 6 hours (typically 12 to 24 hour release), which restores normal vascular tone in an affected local vascular bed, such as the pudendal or penile vasculature of men with ED, without inappropriately affecting systemic vascular tone, and preferably, but not necessarily, without inducing tolerance to the effects of a NO releasing compound and/or biotransformation of a NO releasing compound to its releasing form.
According to a further aspect of the present invention there is provided a method to treat female sexual dysfunction (SD) wherein the method comprises administration of NO or one or more NO donors, or one or more agents which activate guanyl cyclase, by oral, sublingual, buccal, intravenous, transdermal, or any other effective route, in concentrations that are about xc2xd to about {fraction (1/20)} of a concentration required to induce vasodilation in xe2x80x9chealthyxe2x80x9d or normal regions such as the coronary or skeletal muscle vasculature.
According to yet a further aspect of the present invention there is provided a method to treat SD comprising administering to a subject in need thereof a quantity of GTN by any route, for example, oral, sublingual, transdermal, intravenous, or inhalation, that provides plasma concentrations of below about 250 pg/ml of the GTN, so that SD is treated.
According to one aspect of the present invention there is provided a low-dose transdermal xe2x80x9cpatchxe2x80x9d with short term release of, for example, GTN, or any other effective provider of NO such as, for example, one or more NO donors or one or more agents which activate guanyl cyclase, over a period of time less than 6 hours (as opposed to 12, 18 or 24 hour release), which restores normal vascular tone in an affected local vascular bed, such as the pudendal, cervical or vaginal vasculature of women with SD, without inappropriately affecting systemic vascular tone or causing hypotension, and preferably, but not necessarily, without inducing tolerance (Bennett et al., Circ. Res. 63:693, 1988) to the effects and/or biotransformation of a NO releasing compound to its releasing form.
According to a further aspect of the present invention there is provided a low dose or microdose xe2x80x9cpatchxe2x80x9d with long term release of, for example, GTN, or any other effective provider of NO, such as, for example, one or more NO donors or one or more agents which activate guanyl cyclase, over a period of time greater than 6 hours (typically 12 to 30 hour release), which restores normal vascular tone in an affected local vascular bed such as the pudendal, cervical or vaginal vasculature of women with SD without inappropriately affecting systemic vascular tone, nor inducing tolerance to the effects of a NO releasing compound and/or biotransformation of a NO releasing compound to its releasing form.
xe2x80x9cApplying various forms of NOxe2x80x9d as used herein includes administering NO donor or NO producing agents.
xe2x80x9cEnhancing penile erectionxe2x80x9d as used herein is understood to mean increasing physical size and improving tumescence and/or rigidity of a penis, preferably so that it is capable of intromission.
xe2x80x9cErection of good qualityxe2x80x9d and xe2x80x9ceffective erectionxe2x80x9d are used herein interchangeably to mean adequate for vaginal penetration (i.e., intromission, or intercourse).
xe2x80x9cNO donorxe2x80x9d, xe2x80x9cNO producing agentxe2x80x9d, xe2x80x9cNO delivering compoundxe2x80x9d, xe2x80x9cNO generating agentxe2x80x9d and xe2x80x9cNO providerxe2x80x9d are used interchangeably in this specification and include all compounds which donate NO through biotransformation, compounds which generate NO spontaneously, compounds which spontaneously release NO, or any other compounds which otherwise generate NO or an NO-like moiety and include: glyceryl trinitrate, isosorbide 5-mononitrate, isosorbide dinitrate, pentaerythritol tetranitrate, erythrityl tetranitrate, sodium nitroprusside, 3-morpholinosydnonimine molsidomine, S-nitroso-N-acetylpenicillamine, S-nitrosoglutathione, N-hydroxy-L-arginine, S,S-dinitrosodithiol, or NO gas, or a functional equivalents thereof. In some cases, NO is generated by activation of guanyl cyclase.
xe2x80x9cPenisxe2x80x9d as used herein may be interpreted to apply equally to clitoris in so far as there is substantial equivalence between penile and clitoral erectile tissue. xe2x80x9cSexual dysfunctionxe2x80x9d (SD) as used herein includes aspects of female dysfunction and urogenital aging such as decreased vaginal lubrication, decreased vaginal engorgement, pain during intercourse such as, for example, dyspareunia, urogenital infections; and urogenitalia as affected by post-menopause, diabetes, vascular disease, estrogen depletion conditions, sexual dysfunction, and idiosyncratic vaginal dryness, respectively.
xe2x80x9cVarious forms of NOxe2x80x9d as used herein is understood to mean any one of NOxc2x7, NO+ and NOxe2x88x92, preferably NO+ and NOxe2x88x92, and can include as an alternative CO (carbon monoxide) in its various forms, which produces an equivalent effect to NO.
xe2x80x9cWithout inappropriately affecting systemic vascular tonexe2x80x9d as used herein means not affecting mean arterial pressure so as to produce inappropriate systemic vasodilation with effects such as hypotension, headache, flushing.